Method for producing a useful carbon aggregate from a puffing petroleum coke

ABSTRACT

A useful carbon aggregate is produced. The aggregate is made from heat-treated and/or graphitized &#39;&#39;&#39;&#39;puffing&#39;&#39;&#39;&#39; petroleum coke which has been heated in the presence of a puffing inhibiting agent. The heat-treated coke is advantageously employed as an aggregate in the production of graphite bodies whose thermal shock resistance properties are enhanced thereby.

United States Patent [72] Inventors LesllelLJuel Lewlston; Robert W. Rosene, Grand Island, both of N.Y.

[2|] AppLNo. 861,998

[22] Filed Sept. 29, 1969- [45] Patented [73] Assignee Nov. 30, 1971 Great Lakes Carbon Corporation New York, N.Y.

Original application May 29, 1969, Ser. No. 833,851, now Patent No. 3,506,745, dated Apr. 14, 1970. Divided and this application Sept. 29, 1969, Ser. No. 861,998

[54] METHOD FOR PRODUCING AUSEFULCARBON AGGREGATE FROM A PUFFING PETROLEUM COKE 2 Claims, No Drawings [52] US. Cl 106/307, 23/209. 1 23/2099, 264/29 [51] lnt.Cl C09cl/44 [50] FieldofSearch 23/2099, 209.1, 209.2; 264/129; 201/17; 106/307 [56] Relerences Cited UNITED STATES PATENTS 2,814,076 I 1/1957 Gartland 264/29 3,338,993 8/1967 .luel et al..... 264/29 3,369,871 2/1968 Hardy et al. 23/2099 Primary Examiner-Edward J. Meros AttorneyWallace F. Neyerlin METHOD FOR PRODUCING A USEFUL CARBON AGGREGATE FROM A PUFFING PETROLEUM COKE This application is a divisional application of application Ser. No. 833,851, filed May 29, 1969 and issued Apr. 14, 1970 as U.S. Pat No. 3,506,745.

This invention relates primarily to the production of a useful carbon aggregate from a puffing petroleum coke and to the field of electric furnace electrodes although it also applies to the general field manufactured carbon and graphite articles.

Under the pressure of strong competition from the basic oxygen furnace (BOF) and similar, newly developed steel making processes, the electric furnace operators have been forced to develop ways and means of reducing costs. This has been achieved largely by greatly increasing the rates of melting through the use of higher powered furnaces. As a consequence, the service demands placed upon the electric furnace electrodes has greatly increased, and electrodes having much higher current carrying capacities are now required. This alone would not be too difficult except for the fact that the thermal shock and oxidation resistance of these superconductors must also be substantially maintained if not improved.

Electrodes required for these higher powered electric furnaces are at least about 14 inches in diameter and at least about 5 feet in length and in order to get the maximum utilization from the electrodes high current densities between about 125 and about 200 amperes per square inch are employed. Modern, large-size, steel-producing electric furnaces of high productive capacity more typically require that such electrodes be about 24 inches in diameter and about 6 feet to about 9 feet in length. Such electrodes typically have threaded sockets and are coupled together by threaded nipples in order to make up the electrode column used in the electric furnace (e.g. typically about three electrodes in the column). The assemblage of an electrode column which will perform satisfactorily while carrying these required or desired high currents while at the same time being subjected to the sever service demands such high-powered furnaces impose has not been generally achieved in the past. Socket splitting, nipple breakage, spalling, and excessive pencilling (due to oxidation) have been quite common.

It is a finding of this invention that electrodes of high density and strength, high electrical conductivity (or low resistivity), high thermal shock resistance and low oxidation loss can best be achieved by producing the electrodes from an aggregate comprised in part or in total of a heat-treated and/or graphitized puffing" petroleum coke which has been heated in the presence of a puffing inhibiting agent in order to inhibit its pufiing. It is important that it be clearly understood that the petroleum coke which is graphitized, or which is heated sufficiently high in the presence of a puffing inhibiting agent to inhibit its puffing, is petroleum coke as such and not petroleum coke which has had its characteristics materially altered such as by procedures which are standard in the art.

It is standard practice in the production of electric furnace electrodes or other carbon and graphite bodies to use calcined (viz raw petroleum coke heated to temperatures between about l,200 C. and about 1,400 C.) petroleum coke as the aggregate in the production of electrodes and to mix this aggregate with a carbonaceous binder such as pitch. The mixture typically is then formed, such as by extrusion, baked, and if desired, graphitized. if high density and high electrical conductivity are desired, these properties have typically been achieved by employing one or more pitch impregnations at some point after the initial baking operation.

it is also common practice to employ scrap graphite" in the aggregate in the production of electrodes or other carbon and graphite bodies. Scrap graphite is defined as lathe tumings and other byproducts from the machining of graphite products as well as any reject material generated in connec' tion with the graphitization of articles made from calcined petroleum coke and a binder.

It will be noted that in said prior art standard practices the petroleum coke is used with another material such as pitch before the petroleum coke is heated to temperatures above standard calcining temperatures. Consequently, neither of the foregoing standard prior art practices employ petroleum coke in the same manner as it is employed and as described herein. By using petroleum coke, processes as described herein, and specifically claimed, either alone or in part in the aggregate, carbon and graphite articles of high density and electrical conductivity can be achieved without loss in thermal shock resistance.

It is known that most petroleum cokes, especially those of the so-called needle type as defined in the Shea patent (U.S. Pat. No. 2,775,549 undergo "puffing" or expansion when heated to temperatures above at least about 1,400 C., such as when, for example, they are heated through the temperature range of about l,400 to 1,800 O, as of course is the case if they are heated to 2,000 C. and higher. This puffing does not occur during normal calcining or baking operation. If this pufl'mg is not inhibited or prevented, the petroleum coke when heated to such temperatures as indicated will possess a low bulk density. If this occurs many of the advantages of using this type of aggregate are lost and the properties sought in the. baked and/or graphitized electrodes to be produced will not be achieved. This results primarily from the fact that the low bulk density material requires excessive amounts of binder to form a suitable mix for forming, and even if such a mix is formed by extrusion or molding, subsequent processing is difficult, and also a low density, low strength product typically results.

To eliminate or substantially reduce this puffing, it is a finding of this invention that those puffing inhibitors or puffing inhibiting agents normally added to the mix formulation to inhibit puffing or an article to be baked and/or graphitized can be admixed with the granular petroleum coke itself prior to or during the heating to the puffing and higher temperatures; and that employing the pufiing inhibiting agent(s) in this manner, in contrast to inhibiting the puffing of the formed articles made from the petroleum coke, leads to several processing and product advantages over the latter prior art technique of using puffing inhibiting agent(s). If the inhibiting agent is introduced during the heating of the granular petroleum coke, the time of introduction must be such that the temperature is still below the point where puffing begins.

The granular petroleum coke" being discussed is solid petroleum coke which results from the thermal cracking and polymerization of heavy petroleum residues such as reduced or top crudes, thermally or catalytically cracked residuums, etc. The coking is normally conducted in a vertical cylindrical drum such as those manufactured by Keilogg, Lummus and Foster Wheeler Companies. The heavy hydrocarbons are admitted into the drum at a temperature between 875 and 950 F., and are permitted to soak and carbonize until the drum is nearly filled with a solid coke. The material is removed from the drum by various decoking methods known to the art. The material removed from the coking drum will vary widely in particle size. Generally, however, at least about 40-50 percent of it will be retained on a 14-inch screen. The granular petroleum coke may be either the raw coke, viz the coke as it is removed from the coking drum and which typically has a volatile matter (VM) content of about 8 to about 20 percent, or it may be calcined petroleum coke, viz raw petroleum coke which has been heated to no higher than about l,400 C. and to a VM content of less than about 1 percent.

The volatile matter being discussed here is determined by ASTM method D 271-48 modified for sparking fuels" and is exclusive of the moisture and free oil which would be removed by heating to temperatures of 400500 F. Volatile matter is detennined in a platinum crucible in an electrically heated furnace maintained at temperatures of l,742i36 F. A one gram sample of dry 60 mesh coke is preheated at temperatures below l,742 F. and then kept at a temperature of l,742fl6F. for 6 minutes and the resulting weight-loss is termed volatile matter. In any case, the petroleum coke itself is subjected to the process steps described herein, rather than petroleum coke after it has been mixed with a binder and then formed, prior to being baked and/or graphitized, etc.

minus 200 mesh, and can be dusted on'the coarser petroleum coke. lf spraying is to be used, a slurry composed of one part of inhibiting agent (e.g. iron oxide) to two parts water can be prepared and then sprayed on the coke using about 1.1 part by weight of iron oxide for each iOQ parts of coke. if impregna- I tion is employed, inhibiting agents in solution can be used. if mechanical mixing is employed, any mechanical mixer which wili'bring about substantially uniform and intimate blending of the inhibiting agent with the coke in the desired proportions can be used. Y

The amount of inhibitor required in any of the contacting" procedures such as just discussed will depend upon the magnitude of the puffing exhibited by the coke, but will seldom exceed about 3 percent by weight of the coke, and will typically be used in such an amount. as to entirely or at least substantially eliminate the puffing of the petroleum coke.

The puffing petroleum coke which has been contacted with the puffing inhibiting agent may be heated in several ways, for example, by conductive heating in a graphite tube furnace or by resistive heating in a suitable graphitizing furnace. in either of these heating techniques the pufiing inhibiting agent can be admixed with the granular petroleum coke prior to or which is made from a puffing petroleum coke and which is emried out in separate baking and graphitizing operations.

. Separate furnaces and intermediate cooling between the baking and graphitizing will also generally be employed in such a process variation. I

It will frequently be desirable to impregnate the carbon body with a carbonaceous binder after it isbaked and before it is graphitized.

The aforedescribed cooled product or carbon aggregate ployed in amounts sufficient to comprise at least percent by weight of the aggregate or carbonaceous filler used in making the fonned article is considered unique with the present invention as are also the process techniques described for making same. i

As previously pointed out, the processing techniques of the present invention are particularly advantageous in the production of electrodes for modern, large-size, steel-producing,

during the heating of the petroleum coke. ln any-case the mixture of the puffing petroleum coke and puffing inhibiting agent is heated in a substantially nonoxidizing atmosphere to a temperature above that at which the coke begins to puff in the absence of said puffing inhibiting agent, and preferably to a temperature at least as high as 2,000 C. Preferably the mixture will be heated to a temperature between about 2,000 C. and about 3,000 C., and,'in some instances, at vary rapid upheat rates such as up to about 10,000 per hour.

After being so heated,'the pufiing petroleum coke is typically cooled to room temperature and an any case to a temperature below about 200 C. so that it can be conveniently handled in the next steps of the process of making carbon and graphite articles. The processes of producing the aggregate and of making the carbon and/or graphite articles may, of course, be carried out by separate parties and at separate sites. These next steps comprise mixing the aforesaid cooled product with a carbonaceous binder such as pitch, forming this petroleum coke-binder product into an article of desired configuration and heating the formed article under nonoxidizing conditions to a temperature at least sufficiently high to carbonize the binder (for example, at least to about 500600 C). Where the article is to be graphitized, it is subjected to a temperature at least as high as about 2,000 C.

Typically other carbonaceous materials can be used as aggregate and mixed with the aforesaid cooled product and binder in making the formed article, but in any event the cooled product will comprise at least 20 percent by weight of the aggregate or carbonaceous filler used in making the formed article in order that the processing and product advantages of the present invention may be achieved to a substantial degree. Preferably the cooled product will be used in such an amount as to comprise at least 50 percent by weight of the aggregate which is mixed with the carbonaceous binder.

Because part or all of the carbonaceous filler used in making the formed article has been heated to a very high temperature, e.g. higher than conventional calcining or baking temperatures and at least to a temperature above that at which the petroleum coke begins to puff, and preferably above 2,000 C., the carbon article or body produced when it is heated to a temperature sufiicient to carbonize the binder can also be referred to as a semi-graphite carbon body. The article or body produced when the formed article is heated to a temperature at least as high as about 2,000 C., is referred to herein as a graphite body.

if the article is heated to a temperature at least as high as about 2,000 C.," the heating of the same will typically be carelectric furnaces of high productive capacity wherein the electrodes have to be of substantial dimension as previously described and wherein they are subjected to high current densities in excess of about amperes per square inch. These techniques have minimized processing losses, enabled greater product uniformity, and reduced processing times and costs and have also resulted in electrodes of improved thermal shock resistance at high levels of density, strength and electrical conductivity. Large graphite electrodes, which have been made for use on a steel furnace as just described, and which have been made by using puffing petroleum coke whose puffing has been inhibited by the techniques described herein, have been found to be particularly important and valuable articles of commerce. 7

The following examples are illustrative of the improvements attainable through the practice of this invention.

EXAMPLE 1 A needle type calcined petroleum coke (all minus 1 inch and determined in advance to be a puffing coke) was heated to 2,900 C. in the presence of 1% percent by weight of finely divided iron oxide powder. The coke was contacted with the iron oxide by the aforedescribed spraying" technique. The heating was conducted over a period of about 8 hours in a neutral or nonoxidizing atmosphere. After cooling, the graphitized coke was crushed and sized to give a particle fraction (minus 4 plus 35 mesh Tyler) and a flour fraction (50 percent minus 200 mesh Tyler). Sixty (60) parts of the particles and 40 parts of the flour were mixed in a steam jacketed mixer with 35 parts of coal tar pitch binder and extruded into 20- inch diameter electrodes. After baking and then graphitizing to 2,700" C., the physical properties of the electrodes were measured. The results are tabulated below. For comparison, a similar mix was prepared from the same original calcined coke using the same particle and flour sizings and the same amount of iron oxide powder and was processed along with the above electrodes. The calcined petroleum coke was not pregraphitized before being mixed with the binder, and extruded, baked and graphitized. The physical properties of these electrodes after graphitization to 2,700 C. were also measured and are tabulated below.

Type o1 carbonaceous aggregate or tiller The dramatic reduction in C.T.E., which indicates a corresponding reduction in susceptibility to thermal shock is of primary significance.

EXAMPLE 2 Using the same formulations as in example 1, extruded electrodes made from calcined coke and from pregraphitized" coke were baked and then pitch impregnated in the standard manner to increase density and strength. After graphitizing these electrodes, their physical properties were measured. The results are tabulated below.

Type of aggregate or filler "Pre-graphi- Calcined tized" Physical Properties gir e t to li as a; cITfEf, 8 1x101 I j g Again, the drastic or dramatic reduction in C.T.E. obtained by using the pregraphitized" coke represents a corresponding improvement in thermal shock resistance.

EXAMPLE 3 Using the procedure of example I, but employing a blend of 60 percent pregraphitized coke particles and 40 percent calcined coke flour in the aggregate, a mix was prepared from 100 parts aggregate and 29 parts of coal tar pitch binder. The

extruded electrodes were baked and pitch impregnated before final graphitization. The following table compares the physical properties of graphitized electrodes similarly processed from 100 percent calcined coke.

Type of aggregate or filler 607 pre graphitlzeii petroleum 1007 coke, 40% itzalglue caltlmied e to cum etro eum Physical properties p coke p coke A.D., gJcc l. 71 1. 70 Res, ohm-111x10 27 22 M.O.R., p.s.i 2,065 2,272 C.I.E., C- X 12.6 7.6

Again, the improvement in C.T.E. attributed to the use of the pregraphitized aggregate is vividly demonstrated.

EXAMPLE 4 Type of aggregate or filler D -gr p 1007 tlzed page]??? 00 e, calclzined rtzaltlalne e to eum Physical properties p coke pe m o e A.D., g./cc 1. 77 1. 74 Res, ohrn-imXlCl 20 20 M.O.R., p.s.i 2,726 2,912 C.'I.E., C- X10 8.2 6.6

The improvement in thermal shock characteristics attributable to the pregraphitized coke is clearly evidenced by the substantial reduction in C.T.E.

The foregoing examples all illustrate the processing of puffing" petroleum cokes, the techniques of using same in acnAIA cordance with the teachings of the present invention, and the advantages of same as graphite articles from pufiing petroleum coke.

EXAMPLE 5 Raw petroleum coke having a volatile matter (VM) content of about 8 percent all minus linch), and which had been detennined in advance to be a puffing" petroleum coke, was heated to 2,500 C. in the presence of lfzpercent by weight of finely divided iron oxide powder. The coke was contacted with the iron oxide by the aforedescribed spraying" technique. The heating was conducted over a period of about 1 1 hours in a neutral or nonoxidizing atmosphere. After cooling, the graphitized coke was crushed and sized to give a particle fraction (minus 4 plus 35 mesh) and a flour fraction (50 percent minus 200 mesh). Sixty (60) parts of the particles and 40 parts of the flour were mixed in a steam jacketed mixer with 35 parts of coal tar pitch binder and extruded into 14- inch diameter electrodes. After baking and then graphitizing to 2,700 C., the physical properties of the electrodes were measured. For comparison, electrodes were made from a similar mix of aggregate, iron oxide powder and coal tar pitch binder in which the aggregate was prepared by first calcining the same original raw petroleum coke to a temperature of about 1.250" C. in a rotary kiln, cooling the calcined coke, and then crushing and milling to give the same particle and flour sizings as above. These electrodes were processed along with the above. The physical properties of these electrodes after graphitization to 2,700 C. are tabulated below.

Type of aggregate or filler Calclned "Pro-graphiraw tized" raw petroleum petroleum This example illustrates that the processing techniques of this invention may be applied to raw petroleum coke as well as to calcined petroleum coke in achieving the improvements described herein.

The inhibition of the puffing of formed articles made from pufiing petroleum coke, previously referred to as a standard prior art procedure, is described, for example, in U.S. Pat. No. 2,814,076, wherein several chemicals used to inhibit puffing are discussed. The particular puffing inhibiting agent(s) employed in the process of the present invention is not considered to be of any patentable significance, although iron oxide is considered as the preferred inhibiting agent. However, the manner in which the inhibitor is employed in the process of the present invention, as described herein and as contrasted with prior art techniques of employing puffing inhibitors, and the improvements achievable thereby, are considered of patentable significance.

Also, the technique of determining whether a petroleum coke "puffs" is not part of the present invention. However, the following explanation of a general or typical procedure employed in making this determination is set forth so that what is meant by this phenomenon will be clarified.

A given portion of the petroleum coke to be tested for puffing" is calcined. Plugs are made from the calcined coke, using a particle mix, baked to 1,000 C. and carefully measured before and periodically during the graphitizing cycle for indications of abnormal thermal expansion, commonly referred to as pufiing. If puffing is indicated, various amounts of pufi'mg inhibitor are added to the mix from which the plugs are made, and the heating process repeated. The amount of inhibiting agent required to eliminate puffing is therefore taken as that amount required to eliminate this abnormal expansion.

We claim:

1. A process for producing a useful carbon aggregate from a 2. A process for producing a useful carbon aggregate from a pufimg petroleum coke which consists in: puffing petroleum coke which consists in:

A. adding a nongaseous puffing inhibiting agent to the A. adding a nongaseous puffing inhibiting agent to the puffing petroleum coke in a ff i t amount to b t puffing petroleum coke in a sufficient amount to substantially eliminate the puffing of the petroleum coke; tially eliminate the puffing of the petroleum coke;

B. heating the coke-inhibiting agent mixture of step A in a B- heating the coke-inhibiting agent mixture of p A in a nonoxidizing atmosphere to a temperature above about "Onoxidizing atmosphere to a temperature at as high 1,400 C. and also above that at which the coke begins to as zvoooo C; and

puff in the absence ofsaicl purrin inhibiting agent; and cooling th Product of p B to a temperature el C. cooling the product of step B to a temperature below 10 about 200 0 about 200C. 0* w i at n 

2. A process for producing a useful carbon aggregate from a puffing petroleum coke which consists in: A. adding a nongaseous puffing inhibiting agent to the puffing petroleum coke in a sufficient amount to substantially eliminate the puffing of the petroleum coke; B. heating the coke-inhibiting agent mixture of step A in a nonoxidizing atmosphere to a temperature at least as high as 2, 000* C.; and C. cooling the product of step B to a temperature below about 200* C. 